Web-guiding device

ABSTRACT

The invention relates to a web-guiding device comprising at least one directing element ( 10 ) for guiding a web in a contactless manner in a machine that is used for producing and/or treating a moved web of material ( 1 ), especially a paper or cardboard web. Said directing element ( 10 ) is provided with a directing surface ( 12 ) that is made at least in part of air-permeable porous material ( 14 ) which can be impinged upon by compressed air so as to form an air cushion ( 18 ) between the directing surface ( 12 ) and the moved web of material ( 1 ) via the air ( 16 ) flowing through said porous material ( 14 ). The directing surface ( 12 ) is divided into at least one web transfer zone ( 2, 4 ) and a web-guiding zone ( 3 ) along the direction of movement ( 2 ) of the web of material. Said zones ( 2, 4; 3 ) are embodied so as to allow for a different air throughput.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. National Stage of International PatentApplication No. PCT/EP2004/051099 filed Jun. 14, 2004, and claimspriority of German Patent Application No. 103 39 262.9 filed on Aug. 26,2003.

BACKGROUND OF INVENTION

1. Field of the Invention

The invention relates to a web-guiding device comprising at least oneguide element for non-contact web guidance in a machine used forproducing and/or treating a moving material web, in particular a paperor board web. It relates further to a machine for producing and/ortreating a material web, in particular a paper or board web, comprisingat least one such web-guiding device.

2. Discussion of Background Information

In the past, the material web has been guided by means of guide rolls,in which contact with the surface and a drive are absolutely necessary.Such web guidance is, however, relatively complicated and expensive. Theweb has to be pulled off the surface of such guide rolls, for whichpurpose appropriate pulling-off forces have to be applied.

Additionally, the material web has been led over an airturn. In thiscase, although non-contact guidance with a stationary guide element ispossible, as a rule a nonuniform pressure prevails in the air cushion.In the event of holes or partial breaks, the web can thereforenevertheless contact the guide element. In addition, no reliable, flatand crease-free web guidance is ensured. For example, it is possible inparticular for omega creases, as they are known, to occur. Correspondingweb guidance is again known to be expensive. Large quantities of air andlarge dimensions are necessary.

An airturn, as it is known, normally has slot nozzles with a mutual slotnozzle spacing of about 20 to about 200 mm and a respective slot widthwhich is greater than 1 mm. If rows of nozzle holes are provided, thenozzle hole diameter is generally greater than 2 mm. The web spacingfrom the surface is generally greater than 5 mm, normally lying in arange from 7 to 20 mm. The pilot pressure in the airturn is generally ina range from 1 to 6 kPa (=0.06 bar). The specific volume flow isnormally in a range from 1000 to 30,000 Nm³/h·m².

SUMMARY OF THE INVENTION

Therefore, the instant invention provides an improved web-guiding deviceof the type mentioned at the beginning in which the aforementioneddisadvantages are eliminated. In particular, stable, crease-free andreliable non-contact web guidance is intended to be achieved. It isintended in particular for use in paper machines, coating machines,calenders, slitter-rewinders and so on to be possible.

According to the invention, the object is achieved in that the guideelement has a guide surface which is at least partly composed of anair-permeable porous material to which compressed air is applied, inorder via the air flowing through this porous material to form an aircushion between the guide surface and the moving material web, and inthat the guide surface is divided along the direction of movement of thematerial web into at least one web transition zone and one web-guidingzone, which are designed for a different air throughput.

The high pressure loss at the porous material produces a very uniformair cushion, so that the material web is guided reliably at a relativelysmall distance from the surface. This is associated in particular with acrease-free run. The relatively high internal pressure prevents any webcontact with the surface.

The web-guiding device can therefore in particular comprise at least oneguide element, which is supplied with compressed air and has an opensurface but with a high pressure loss, through which air is forced fromthe interior. Therefore, in terms of both time and space, a stableuniform air cushion is produced, which guides the web, for example, in apaper machine, a coating machine, a calender, a slitter-rewinder and soon, without contact with the guide element.

Here, provision is made for the part of the guide surface to whichcompressed air is applied to be subdivided into at least one webtransition zone and one web-guiding zone. The web transition zone is aregion which is limited with respect to the direction of movement of thematerial web about the geometric point on the guide surface at which thematerial web runs on or runs off. The web-guiding zone extends in orcounter to the direction of movement adjacent to the web transitionzone, and it is used for the actual air-cushioned guidance of thematerial web. Both the at least one web transition zone and theweb-guiding zone have compressed air applied to them but a different airthroughput being provided for the different zones.

Since the air cushion explained is produced along the web transfer zonebecause of a different air throughput than along the web-guiding zone,firstly, at the point on the guide surface at which the material webruns on and/or off, the air cushion can be maintained in a stablemanner, although in this zone the slot formed by the material web andthe guide surface enlarges and, consequently, air can escape from theweb-guiding zone in this region. In other words, the air cushion is keptstable even in its edge region, so the material web does not undesirablycome into contact with the guide surface, even at the point at which itruns on and runs off.

Secondly, this non-contact web guidance does not require anyspecifically increased consumption of compressed air, since a modifiedair throughput has to be provided only for the web transition zone, thatis to say for the surroundings of the point on the guide surface atwhich the web runs on and runs off. The web-guiding zone, on the otherhand, can be supplied with an air throughput which is different fromthis and suitable to form the air cushion. This makes it possible forthe thickness of the air cushion which is formed between the guidesurface and the moving material web to be stabilized to a value of, forexample, less than 5 mm, in particular less than 3 mm.

In particular, a higher air throughput can be provided in the webtransition zone than along the web-guiding zone. An increased airthroughput in the web transition zone can prevent undesired contactbetween the material web and the guide surface particularly effectivelyif, because of the escape of compressed air in the edge region of theair cushion formed, there is a particularly increased risk of suchcontact.

The aforementioned web transition zone is preferably a web run-on zone,that is to say a region in the vicinity of the geometric point at whichthe material web runs onto the guide surface, since in this region theavoidance of undesired contact between the material web and the guideelement is particularly important. As an alternative to this, however,the web transition zone can be provided as a web run-off zone only inthe region of the point at which the material web runs off.

As an alternative to this, it is possible for the guide surface to haveat least two web transition zones, namely at least one web run-on zoneand one web run-off zone, between which—relative to the direction ofmovement of the material web—the web-guiding zone is arranged. In thiscase, both web transition zones have a different air throughput, inparticular a higher air throughput, than the web-guiding zone. In thiscase, it is possible for the web run-on zone and the web run-off zone tobe designed for a different air throughput relative to each other aswell, which is in particular in each case higher than the air throughputprovided along the web-guiding zone.

The different air throughput can be implemented by the porosity of theweb transition zone or a plurality of web transition zones, on the onehand, and the porosity of the web-guiding zone, on the other hand, beingdifferent. For instance, the web transition zone can have a higherporosity than the web-guiding zone, in order to implement a higher airthroughput in the web transition zone. In particular, the porosity ofthe web transition zone can be higher by a factor of at least 1.5,preferably by a factor 2, than the porosity of the web-guiding zone.

Given such a different porosity, the web transition zone and theweb-guiding zone can have the same air pressure applied to them, acommon compressed air supply preferably being provided. Alternatively oradditionally to this, however, it is also possible for the webtransition zone or web transition zones, on the one hand, and theweb-guiding zone, on the other hand, to have compressed air applied tothem at different pressure, in order to bring about a different airthroughput. The difference in the application of the compressed airbetween the web transition zone and the web-guiding zone, that is to saythe pressure difference on the inside of the guide surface, can be forexample at least 2 bar, in particular at least 4 bar. The different airpressure is preferably produced by at least two separate compressed airsupplies.

According to one embodiment of the invention, provision is made for theguide surface to be curved and for the web transition zone—along thedirection of movement of the material web and relative to the radius ofcurvature of the guide surface—to extend over a segment angle of atleast +/−5°, preferably between +/−10° and +/−20°, about the geometricpoint at which the material web runs on and/or off the guide surface. Inother words, the relevant web transition zone is restricted with respectto the segment angle to a region in the vicinity of the point at whichthe material web runs on and/or off the guide surface. In other words,with respect to the segment angle, the relevant web transition zone isrestricted to a region in the vicinity of the run-on point or therun-off point, this segment angle relating to the main radius ofcurvature in the case of a varying curvature. In this embodiment,provision can be made for the web transition zone to extend over anasymmetric segment angle about the geometric run-on point or run-offpoint, for example by a segment angle of −10°/+5° or of −15°/+20°.

The guide element preferably comprises at least one pressure chamber,via which compressed air can be applied to the porous material. In thiscase, the porous material can at least partly be applied to a carriercontaining the pressure chamber and provided with air passage openings.However, for example, such embodiments in which the porous materialforms at least part of the pressure chamber wall are also conceivable.The pressure chamber can supply the web transition zone and theweb-guiding zone simultaneously with compressed air, or an individualpressure chamber is provided for each zone.

The pressure in the pressure chamber can in particular be higher than0.5 bar, preferably being higher than 1 bar.

The specific volume flow in the porous material expediently lies in arange from about 10 to about 5000 Nm³/h·m².

The hole or pore spacing or the distance between the outlet openings inthe air-permeable porous material is preferably less than 1 mm.

The porous material is in particular composed in such a way that noindividual jets but, instead, a very uniform air cushion is produced,which ensures very good web guidance which, in particular, remainscontact-free in any case even in the event of holes, tears or thinstrips. In one preferred practical embodiment of the web-guiding deviceaccording to the invention, the average size of the outlet openings,pores and/or holes in the porous material is less than 0.2 mm andpreferably less than 0.1 mm.

The porous material is preferably chosen such that a high pressure lossfrom the interior to the surroundings results, which produces a veryuniform air cushion.

In an expedient practical embodiment of the web-guiding device accordingto the invention, the pressure loss, in particular from the side facingaway from the moving material web toward the side of the porous materialfacing the material web, is greater than 0.2 bar and preferably greaterthan 0.8 bar.

The guide element can be designed in particular as a roll. In this case,this can be designed as a stationary or nonrotating roll or a rotating,preferably driven, roll. In the case of a rotating roll, the differentair throughput is preferably brought about by the web transition zoneand web-guiding zone, arranged to be stationary and having the sameporosity, having a different air pressure applied to them.

In particular in the case in which the guide element is designed as astationary or nonrotating roll, the air cushion is advantageouslyproduced only on part of the roll circumference.

The roll can have, for example, a diameter in a range from about 50 mmto about 1500 mm.

It is also advantageous in particular if the guide element is designedas a segment of a curve. In this case, it can have a radius of curvaturethat is constant in the direction of movement of the material web or aradius of curvature that changes in the direction of movement of thematerial web. In the latter case, the guide element can have a radius ofcurvature that changes continuously in the direction of movement of thematerial web or a radius of curvature that changes in discrete steps inthis direction of movement.

In order to produce a spreading effect, the guide element or its guidesurface can in particular also have a course that is curved in thetransverse direction. In this case, the radius of curvature of the guideelement or of the guide surface can change over the width extending inthe transverse direction.

The radius of curvature of the guide surface expediently lies in a rangefrom about 5 to about 3000 mm.

According to an advantageous development of the invention, the guidesurface of the guide element is also subdivided transversely withrespect to the direction of movement of the material web into aplurality of zones, which are designed for a different air throughput.For instance, one or two peripheral zones can have a higher airthroughput than a central zone of the guide surface, in order tocompensate for lateral escape of the compressed air. The different airthroughput can be effected by means of different porosities of the zonesand/or by applying compressed air to the various zones at a differentair pressure.

In a preferred practical embodiment of the web-guiding device accordingto the invention, the guide element is assembled from a plurality ofindividual segments in the direction of movement of the material weband/or in the direction transverse hereto. In this case, at least someof the segments can be assigned a common compressed air supply. However,the segments can also be at least partly supplied via separatecompressed air supplies.

In a further advantageous embodiment of the web-guiding device accordingto the invention, the guide surface of the guide element is formed by atleast two layers consisting at least partly of air-permeable porousmaterial and preferably having different properties.

In this case, the pressure loss on the inner layer facing away from thematerial web can be lower than on the outer layer. Alternatively oradditionally, the porosity of the inner layer facing away from thematerial web can be higher or its hole spacing can be greater than inthe outer layer. Alternatively or additionally, the hole diameter on theinner layer facing away from the material web can be greater than on theouter layer. It is also advantageous in particular if the layers consistat least partly of different material.

A further preferred embodiment of the web-guiding device according tothe invention is distinguished by the fact that the inner layer facingaway from the material web consists of air-permeable porous material oris provided with air passage openings only in a subregion and isotherwise air-impermeable, so that an air cushion is produced only in asubregion of the guide element.

The inner layer facing away from the material web can consist at leastpartly of metal, GRP and/or CRP in particular.

The inner layer facing away from the material web preferably suppliesthe mechanical loadbearing capacity of the guide element or the guidesurface.

The outermost surface of the guide element facing the material web canin particular consist of fine-pore material. It can therefore inparticular have a finer level of porosity than the inner layer.

It is also advantageous in particular if the outermost surface of theguide element facing the material web is sintered.

This outermost surface of the guide element facing the material web canconsist, for example, of ceramic or sintered ceramic material, inparticular of silicate ceramic, oxide ceramic or nitride ceramicmaterial.

The guide surface of the guide element is advantageously provided withair outlet openings preferably produced directly during the productionof the outermost surface. The relevant air outlet openings therefore donot have to be introduced into the outermost surface by means ofsubsequent machining.

As already mentioned, the web-guiding device according to the inventioncan be used in particular in a machine for the production and/ortreatment of a material web, in particular a paper or board web.

Thus, for example, at least one appropriate web-guiding device can beprovided after the press section, preferably immediately thereafter. Anappropriate web-guiding device can therefore be provided, for example,as a substitute for a conventional paper guide roll after the press,that is to say in a region of a web which is still very wet andsensitive. This is associated with the advantage that the web no longerhas to be pulled off and a drive is dispensed with.

It is also advantageous if at least one appropriate web-guiding deviceis provided in a machine section in which there is an already largelydry material web. The web-guiding device according to the invention cantherefore, for example, be provided as a substitute for a conventionalpaper guide roll in the case of a largely dry web. This is again alsoassociated with the advantage that no drive is required, that is to sayit is no longer necessary for all the guide rolls to be driven but onlythose which are important for the web tension.

Advantageously, at least one appropriate web-guiding device is providedimmediately after the last drying cylinder.

In particular, at least one appropriate web-guiding device can also beprovided in each case before and/or in a calender. In this case, arespective web-guiding device can again be arranged immediately beforeor immediately after the calender.

Moreover, for example a use before a winder and/or before an unwind isalso conceivable. In this case, the respective web-guiding device can,for example, again be arranged immediately before the winder or unwind.

In principle, at least one appropriate web-guiding device can in eachcase also be provided in a coating machine and/or in a slitter-rewinder.

It is also advantageous in particular if at least one appropriateweb-guiding device is provided after a surface coating means, inparticular as a substitute for an airturn. As a result of the small webspacing and the uniform air cushion, crease-free guidance is alsoensured here. Further advantages result from the low quantity of air andthe smaller overall volume.

In an advantageous practical embodiment, at least one appropriateweb-guiding device is provided as a substitute for a respective spreaderroll.

Inter alia, is also advantageous if at least one appropriate web-guidingdevice is provided directly before and/or after an air dryer. In thiscase, at least one appropriate web-guiding device can in each case beprovided, for example, directly before and/or after an impingement dryerin a drying section and/or in a coating machine or afterdryer section.

It is also advantageous in particular if at least one appropriateweb-guiding device is provided as a supporting element in a two-rowdrying group, in the free draw between the cylinders. In this case, ofcourse, appropriate web-guiding devices can also be provided in aplurality of such two-row drying groups.

If the relevant guide element is provided as a rotatably mounted roll,then the result is, moreover, good emergency running properties since,even in the event of failure of the pressure supply, it is not possiblefor friction to occur between the material web or a moving belt, forexample a fabric belt, and the rotating roll.

The guide element can, for example, be wrapped around only by thematerial web or, in addition to the material web, for example can bewrapped around by at least one fabric belt.

The material web or the moving belt can wrap around the guide element,for example, in accordance with a wrap angle whose range runs from about5 to about 260°.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is further described in the detailed descriptionwhich follows, in reference to the noted plurality of drawings by way ofnon-limiting examples of exemplary embodiments of the present invention,in which like reference numerals represent similar parts throughout theseveral views of the drawings, and wherein:

FIG. 1 depicts a schematic cross-sectional illustration of guideelements used for non-contact web guidance having a guide surfaceconsisting at least partly of porous material,

FIG. 2 depicts a schematic cross-sectional illustration of furtherembodiments of the guide element which, for example, are designed in theform of a segment of a curve,

FIG. 3 depicts a schematic cross-sectional illustration of guideelements used for non-contact web guidance having a guide surfaceconsisting at least partly of porous material,

FIG. 4 depicts a schematic cross-sectional illustration of furtherembodiments of the guide element which, for example, are designed in theform of a segment of a curve,

FIG. 5 depicts a schematic longitudinal sectional illustration of afurther embodiment of the guide element which is subdivided in thetransverse direction into at least two zones or segments, the varioussegments having the same pressure applied to them in the present case,

FIG. 6 depicts an embodiment of the guide element comparable with theembodiment according to FIG. 5 but the various segments having adifferent pressure applied to them in the present case,

FIG. 7 depicts a schematic illustration of a guide element that his bentin the transverse direction and, for example, can be used for spreading,and

FIG. 8 depicts a schematic illustration of a preferred embodiment inwhich a guide element is provided after an applicator as a substitutefor an airturn.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The particulars shown herein are by way of example and for purposes ofillustrative discussion of the embodiments of the present invention onlyand are presented in the cause of providing what is believed to be themost useful and readily understood description of the principles andconceptual aspects of the present invention. In this regard, no attemptis made to show structural details of the present invention in moredetail than is necessary for the fundamental understanding of thepresent invention, the description taken with the drawings makingapparent to those skilled in the art how the several forms of thepresent invention may be embodied in practice.

FIG. 1 shows, in a schematic cross-sectional illustration along thedirection of movement L of a material web 1, an embodiment of a guideelement 10 of a web-guiding device used for non-contact web guidance,which in particular can be used in a machine which is used for theproduction and/or treatment of a material web, for example a paper orboard web. Such a guide element 10 can in particular be provided afteran applicator as a substitute for an airturn (cf. also FIG. 8).

The guide element 10, designed in the present case in the form of aroll, for example, has a guide surface 12 which consists ofair-permeable porous material 14, to which compressed air can be appliedfrom the inside in order to form an air cushion 18 via the air 16flowing through the porous material 14 and the moving material web 1.

The guide surface 12 of the guide element 10 is subdivided along thedirection of movement L of the material web 1 into a first webtransition zone, specifically a web run-on zone 2, furthermore into aweb-guiding zone 3 which follows the former and, following the latter,into a second web transition zone, namely a web runoff zone 4. The webrun-on zone 2 and the web run-off zone 4 of the guide surface 12 aredesigned for a higher throughput of the air 16 flowing through than theweb-guiding zone 3 arranged between them, as is indicated in FIG. 1 bythe density of the arrows which symbolize the air 16 flowing through.

In particular in the case in which the guide element 10 shown isdesigned as a stationary roll, the different air throughput is broughtabout by means of a different porosity of the porous material 14 in thedifferent zones 2, 3, 4. On the other hand, if the guide element 10 isdesigned as a rotating roll, then the different air throughput iseffected, for example, by the rotating roll shell having a uniformporosity but the application of compressed air at different intensitiesbeing carried out within the different zones 2, 3, 4. Otherwise—inparticular in the case of a guide element 10 arranged to be stationary—adifferent air throughput in the different zones 2, 3, 4 can also beeffected by a combination of different porosities in the zones 2, 3, 4of the guide surface 12 with a different application of air pressurealong the different zones 2, 3, 4.

The web run-on zone 2 extends on the guide surface 12 along a segmentangle of a total of 20° symmetrically about the geometric point 5 atwhich the material web 1 runs on, that is to say about that point atwhich the material web 1 contacts the guide surface 12 tangentially. Theweb run-off zone 4 extends on the guide surface 12 along a segment angleof 20° symmetrically about the geometric point at which the material web1 runs off, i.e. at which the material web 1 is separated from thecurved guide surface 12 in the tangential direction. Outside the webrun-on zone 2, the web-guiding zone 3 and the web run-off zone 4,compressed air does not flow through the guide element 10.

By means of the air cushion 18, the material web is guided withoutcontact at a short distance from the guide surface 12. The constructionof the guide surface 12 with the porous material 14 in this case ensuresa particularly uniform build-up of the air cushion 18, so that afault-free and crease-free run of the material web 1 is effected.

The higher air throughput in the web run-on zone 2 and the web run-offzone 4 has the effect that, in the vicinity of the run-on point 5 and ofthe run-off point 6, there is no undesired pressure drop at the surfaceof the guide element 10. Thus, even in these regions of the guideelement 10, non-contact guidance of the material web 1 is ensuredwithout an unnecessarily high consumption of compressed air having to beaccepted for this purpose along the entire guide surface 12 and inparticular within the web-guiding zone 3.

For this purpose, it is possible, for example, for the web run-on zone 2and the web run-off zone 4 to have a porosity higher by a factor of 1.5than the web-guiding zone 3, and/or for the application of compressedair to the web run-on zone 2 and the web run-off zone 4 on the inside ofthe guide surface 12 to be higher than along the web-guiding zone 3.

Otherwise, it is also possible, within the web run-on zone 2, for theair throughput to rise continuously counter to the direction of movementL of the material web 1, and/or, within the web run-off zone 4, for theair throughput to rise continuously in the direction of movement L ofthe material web 1, in order to effect a gradual transition to the airthroughput provided within the web-guiding zone 3. Furthermore, thedifferent air throughput in the zones 2, 3, 4 can also be varied overtime, in particular by means of a corresponding variation in theapplication of compressed air.

FIG. 2 shows a guide element 10 comparable with the embodiment accordingto FIG. 1, whose guide surface 12 is likewise subdivided into a webrun-on zone 2, a web-guiding zone 3 following the former and a webrun-off zone 4 following the latter. The physical position of thesezones 2, 3, 4 is permanently predefined by means of a different porosityof the guide surface 12. On account of the different porosity, a single,compressed air supply in the interior of the guide element 10 issufficient to bring about a different air throughput in the web run-onzone 2 and the web run-off zone 4 and along the web-guiding zone 3.

FIG. 3 shows a further embodiment of a guide element 10 of a web-guidingdevice used for non-contact web guidance, in a schematic illustration.This guide element 10 is designed in the form of a rotating roll. Theguide element 10 has a guide surface 12 which consists of anair-permeable porous material 14, to which compressed air can be appliedfrom the inside, in order to form an air cushion 18 between the guidesurface 12 and the moving material web 1 via the air 16 flowing throughthe porous material 14.

In the interior, the guide element 10 has three pressure chambers 20,20′, 20″ arranged to be stationary, via which compressed air atdifferent pressure can be applied to the porous material 14. In thisway, the guide surface 12 is subdivided into three stationary zones withdifferent air throughputs, namely into a web run-on zone 2, aweb-guiding zone 3 and a web run-off zone 4.

As illustrated, the guide element 10 can comprise a carrier 24containing the pressure chambers 20, 20′, 20″ and provided with at leastone and preferably a plurality of air passage openings 22, to whichcarrier the porous material 14 is applied. In the present case, thiscarrier 24, which is roll-like here, for example, is completelysurrounded in the circumferential direction by porous material 14.

As an alternative to the configuration as a rotating roll, the guideelement 10 according to FIG. 3 can also be constructed as a stationaryroll having three pressure chambers 20, 20′, 20″, the pressure chambers20, 20′, 20″ and the air passage openings 22 in the carrier 24 beingprovided only along part of the circumference of the guide element 10,so that the air cushion is also produced only along part of thecircumference. The air cushion 18 is expediently produced at least inthe region in which the material web 1 wraps around the guide element10.

On account of the roll-like design, the guide element 10 has a radius ofcurvature in the direction of movement L, in particular also in the wrapregion.

FIG. 4 shows a further embodiment of the guide element 10, which isdesigned here in the form of a segment of a curve, by way of example, ina schematic cross-sectional illustration. Via a single pressure chamber20, compressed air is again applied to the relevant segment, so that air16 flows through the porous material 14 from inside to outside. In thepresent case, too, the porous material 14 is again applied to theoutside of a carrier 24 containing the pressure chamber 20. The wall ofthe carrier 24 or of the pressure chamber 20 is again provided with airpassage openings 22, via which compressed air is applied to the porousmaterial 14 from inside. The porosity of the porous material 14, andthus the respective air throughput, is higher in a web run-on zone 2than along a web-guiding zone 3.

As can be seen from FIG. 4, in the present case the guide element 10 orits guide surface 12 is also again curved in the machine runningdirection or direction of movement L. Just as in the embodimentaccording to FIG. 3, here, too, the radius of curvature is, for example,also constant over the wrap region.

FIG. 5 shows a further embodiment of the guide element 10 in a schematiclongitudinal sectional illustration, that is to say transversely withrespect to the direction of movement of the material web. In this case,the guide element 10 or its pressure chamber is subdivided in thetransverse direction into at least two segments 20′, 20″, via whichcompressed air can be applied, possibly separately, to the porousmaterial 14 in the transverse direction. In the phase reproduced in FIG.5, the zones 20′, 20″ have the same pressure applied to them, at leastto some extent. On the other hand, FIG. 6 shows the same guide element10 in a phase in which the zones or segments 20′, 20″ are currentlyhaving different pressure applied to them.

The pressure can therefore be varied across the width, that is to say inthe transverse direction, in the desired manner, depending on therespective requirements. Otherwise, the guide element 10 can at leastsubstantially again have a construction such as has been described inconnection with the other embodiments.

FIG. 7 shows a schematic illustration of a guide element 10 curved inthe transverse direction and capable of use, for example, for spreading.The guide element again has a carrier 24 having at least one pressurechamber 20, to which the porous material 14 is applied and via whosepressure chamber 20 compressed air is applied to the porous material 14from inside. With appropriate rotation of the guide element 10, forexample the effective bending radius can be changed. Otherwise, thisembodiment again has, at least substantially, the same construction asthe embodiments previously described.

Whereas, in the exemplary embodiments according to FIGS. 3 to 7, theporous material 14 is in each case applied to a carrier 24 provided withair passage openings 22, in principle at least part of a carrier wall orleast part of the pressure chamber 20 can also be formed by the porousmaterial 14.

In the illustration according to FIG. 8, a guide element 101 is arrangedafter the drying section 32 and before an applicator unit 34, a guideelement 102 is arranged as a substitute for an airturn between theapplicator unit 34 and, for example, an impingement dryer 36, and aguide element 103 is arranged after the impingement dryer 36. The guideelements 10 can in particular again be designed in such a way as haspreviously been described, for example by using FIGS. 1 to 7. It is alsopossible, for example, for at least one guide element 10 to be providedin a coating machine, before a winder and/or after an unwind.

It is noted that the foregoing examples have been provided merely forthe purpose of explanation and are in no way to be construed as limitingof the present invention. While the present invention has been describedwith reference to an exemplary embodiment, it is understood that thewords which have been used herein are words of description andillustration, rather than words of limitation. Changes may be made,within the purview of the appended claims, as presently stated and asamended, without departing from the scope and spirit of the presentinvention in its aspects. Although the present invention has beendescribed herein with reference to particular means, materials andembodiments, the present invention is not intended to be limited to theparticulars disclosed herein; rather, the present extends to allfunctionally equivalent structures, methods and uses, such as are withinthe scope of the appended claims. List of designations  1 Material web 2 Web run-on zone  3 Web-guiding zone  4 Web run-off zone  5 Geometricrun-on point  6 Geometric run-off point 10 Guide element 12 Guidesurface 14 Porous material 16 Air flowing through 18 Air cushion 20Pressure chamber 22 Air passage opening 24 Carrier 32 Drying section 34Applicator unit 36 Impingement dryer L Direction of movement of thematerial web

1-35. (canceled)
 36. A web-guiding device comprising: at least one guideelement for non-contact web guidance; wherein the guide element has aguide surface, the guide surface comprising an air-permeable porousmaterial to which compressed air is applied; whereby air flowing throughthe porous material forms an air cushion between the guide surface and amaterial web; and wherein the guide surface is divided along thedirection of movement (L) of the material web into at least one webtransition zone and a web-guiding zone.
 37. The web-guiding device ofclaim 36, wherein the at least one web transition zone has a higher airthroughput than the web-guiding zone.
 38. The web-guiding device ofclaim 36, wherein the web transition zone is one of a web run-on zoneand a web run-off zone.
 39. The web-guiding device of claim 36, whereinthe guide surface has two web transition zones between which, withrespect to the direction of movement (L) of the material web, theweb-guiding zone is arranged.
 40. The web-guiding device of claim 39,wherein the two web transition zones are a web run-on zone and a webrun-off zone, and wherein the web run-on zone and the web run-off zonehave a different air throughput.
 41. The web-guiding device of claim 36,wherein porosity of the at least one web transition zone and porosity ofthe web-guiding zone are different.
 42. The web-guiding device of claim41, wherein the porosity of the at least one web transition zone ishigher than the porosity of the web-guiding zone.
 43. The web-guidingdevice of claim 42, wherein the porosity of the at least one webtransition zone is higher than the porosity of the web-guiding zone by afactor of at least one of at least 1.5 and at least
 2. 44. Theweb-guiding device of claim 36, wherein the at least one web transitionzone and the web-guiding zone have compressed air applied to them at oneof the same pressure and a different pressure.
 45. The web-guidingdevice of claim 44, wherein when different pressure is applied, thepressure difference is one of at least 2 bar and at least 4 bar.
 46. Theweb-guiding device of claim 44, wherein the at least one web transitionzone has compressed air applied to it at a higher pressure than theweb-guiding zone.
 47. The web-guiding device of claim 36, wherein theguide surface is curved and wherein the at least one web transition zoneextends along the direction of movement (L) of the material web, withrespect to the radius of curvature of the guide surface, by a segmentangle of at least one of at least +/−5°, and between +/−10° and +/−20°,about the geometric point at which the material web runs one of on andoff the guide surface.
 48. The web-guiding device of claim 47, whereinthe at least one web transition zone extends by an asymmetric segmentangle about the geometric point at which the material web runs one of onand off the guide surface.
 49. The web-guiding device of claim 36, theguide element further comprising at least one pressure chamber via whichcompressed air can be applied to the porous material.
 50. Theweb-guiding device of claim 49, wherein the porous material is appliedat least partly to a carrier containing the pressure chamber andprovided with air passage openings.
 51. The web-guiding device of claim49, wherein the porous material forms at least part of a pressurechamber wall.
 52. The web-guiding device of claim 36, wherein pressurein an interior of the guide element is at least one of higher than 0.5bar and higher than 1 bar.
 53. The web-guiding device of claim 36,wherein specific volume flow in the porous material is between 10 and5000 Nm³/h·m².
 54. The web-guiding device of claim 36, wherein porespacing of the air-permeable porous material is less than 1 mm.
 55. Theweb-guiding device of claim 36, wherein average size of pores of theporous material is one of less than 0.2 mm and less than 0.1 mm.
 56. Theweb-guiding device of claim 36, wherein pressure loss from a side facingaway from the moving material web toward a side of the porous materialfacing the material web is one of greater than 0.2 bar and greater than0.8 bar.
 57. The web-guiding device of claim 36, wherein the guideelement is a roll.
 58. The web-guiding device of claim 57, wherein theguide element is one of a stationary roll and a nonrotating roll. 59.The web-guiding device of claim 57, wherein the air cushion is producedonly on part of a circumference of the roll.
 60. The web-guiding deviceof claim 57, wherein the guide element is one of a rotating roll and adriven roll.
 61. The web-guiding device of claim 36, wherein the guideelement is a segment of a curve.
 62. The web-guiding device of claim 36,wherein one of the guide element and the guide surface has a coursecurved in a transverse direction.
 63. The web-guiding device of claim36, wherein the guide surface is subdivided transversely with respect tothe direction of movement (L) of the material web into a plurality ofzones, the zones designed for a different air throughput.
 64. Theweb-guiding device of claim 36, the guide element further comprising atleast two segments, the segments at least one of along and transverselywith respect to the direction of movement (L) of the material web. 65.The web-guiding device of claim 36, wherein the guide surface of theguide element comprises at least two layers, each layer consisting atleast partly of air-permeable porous material.
 66. The web-guidingdevice of claim 36, wherein the surface of the guide element facing thematerial web is sintered.
 67. The web-guiding device of claim 36,wherein the surface of the guide element facing the material webcomprises ceramic material.
 68. A machine for at least one of productionof a material web and treatment of a material web, comprising at leastone web-guiding device, the web-guiding device comprising: at least oneguide element for non-contact web guidance; wherein the guide elementhas a guide surface, the guide surface comprising an air-permeableporous material to which compressed air is applied; whereby air flowingthrough the porous material forms an air cushion between the guidesurface and a material web; and wherein the guide surface is dividedalong the direction of movement (L) of the material web into at leastone web transition zone and a web-guiding zone.
 69. The machine of claim68, wherein the guide element is wrapped around by the material web. 70.The machine of claim 68, wherein the guide element is wrapped around bythe material web and by at least one of a moving belt and a fabric belt.